Intracerebral inoculation of Theiler's murine encephalomyelitis virus (TMEV) results in chronic inflammatory demyelination leading to clinical symptoms in susceptible mice. In light of the potential viral etiology and similarities in the immune-mediated pathology and progression of chronic demyelination, this TMEV system is considered to be one of the best animal models for studying human multiple sclerosis (MS). The previous studies in the field are heavily based on CD4+ T cell responses to TMEV capsid epitopes in the periphery. We have recently focused our efforts on analysis of T cells infiltrating the CNS during the course of TMEV-infection in resistant and susceptible mice. Surprisingly, <5% of the CNS infiltrating CD4+ T cells are reactive to the capsid epitopes in susceptible SJL mice, compared to >45% in resistant C57BL/6 mice. The type, nature and reactivity of the remainder of CD4+ T cells in the CNS are unclear at this time. Our preliminary studies suggest that major CNS-infiltrating CD4+ T cells in virus infected susceptible SJL mice recognize non-capsid epitopes residing on viral RNA polymerase (3D). In addition, we have successfully generated I-AS-tetramers, transgenic mice carrying viral capsid protein genes and TCR transgenic mice expressing TMEV capsid-specific TCRs. Thus, further assessment of the reactivity of the Th cells in susceptible SJL mice will be very important in understanding the potential pathogenic mechanisms of demyelination and these studies are now feasible. We hypothesize that T cells in the CNS specific for non-capsid viral antigens following viral infection may play a critical role in protection or pathogenesis. The specific aims for the proposed studies include: 1) Determination of the level, expansion and nature of capsid-specific CD4+ T cells in the CNS and periphery, including activation states and effector functions; 2) Identification of the specificity and nature of non-capsid viral epitope-reactive T cells infiltrating the CNS during TMEV-infection; 3) Assessment of the role of TMEV capsid- and noncapsid-specific T cells in the pathogenesis of demyelination. We believe that our proposed studies will yield important information on the potential control and pathogenic mechanism(s) against virus-induced immune-mediated demyelination, which is a relevant virus model for studying human MS. [unreadable] [unreadable]